This invention relates to a fuel injection valve for internal combustion engines, particularly for diesel engines.
The main function of the fuel injection valve is to atomize a metered amount of fuel and supply it to the correct region in the combustion chamber. The atomization process depends greatly on the injection pressure that is affected significantly by the very small clearance between the nozzle needle valves and its barrel.
Significant leakage through the small clearance between valve and barrel of the nozzle is prevented solely by the excellence of the fit between these parts. Manufactured from alloy steels and lapped together as a mated assembly they are not individually interchangeable. Meeting the tolerances requires a specialized lapping tool and the resulting parts are custom rather than randomly mated. Conventional nozzles are fast wearing owing to the conditions of operation by which the contacting surfaces of the nozzle needle and bushing are compelled to work at high linear speed and at a very high friction. In cases where the engine is running on lighter fuels such as No. 1 diesel, jet fuels or methanol, the low level lubricity of these fuels is conducive to even greater wear, scoring and abrasion between the co-acting needle and barrel surfaces. In its turn this clearance deterioration causes a low injection pressure which leads to a malfunction of the engine.
Several attempts to develop a fuel injection valve with large clearance between the nozzle needle and its barrel are known. These valves have a housing with the nozzle chamber and spring chamber sealed off from one another. The sealing off is effected in these known valves by a disk shaped rubber diaphragms generally secured in the desired position by vulcanization techniques. These valves were disclosed in U.S. Pat. Nos. 1,814,443 (1931) to Morris J. Goldberg, 2,470,717 (1949) to Vincent Palumbo, 2,750,957 (1956) to Bruno Tavola and German Patent 3614564 (1986) to Hafner Gunter. An East German Patent 264055 (1989) to Winkler Bernd and Polster Christfried shows a nozzle where the nozzle needle has a rubber or plastic elastic sleeve and this needle is vulcanized in the needle barrel. The elastic sleeve provides the lift of the needle and completely prevents the fuel leakage along the needle valve. However, those type of fuel valves are not reliable and are expensive to manufacture.
Another problem with the current valves is associated with the fuel injection rate at the early stage of the injection. To satisfy the recent requirements for the cleaning of the exhaust air and the saving of the fuel consumption, it has been found that it is desirable that a rate of injection slowly increases at an early period of the fuel injection process and rapidly decreases at the end.
To meet this requirement several types of the two-stage injectors with reduced fuel injection rate throughout the initial injection stroke have been proposed. For example, in U.S. Pat. Nos. 4,852,808 (1987) to Josshihisa, and 4,913,113 to Georges (1989), in Great Britain Patent 2223798 (1988) to Nicol Stuart William and 2215395 (1988) to Lintoff Edward Robert, in German Patents 3820509 (1988) to Komaroff Iwan et al and 3819814 (1988) to Robert Bosch. However, in these fuel injectors, in contrast to a conventional one, numerous component parts are required and this substantially increases their dimensions, weight and cost. Many of these two-stage injectors have been limited to use only in larger displacement engines.